Bearing assemblies are typically circular in shape, and generally comprise rolling elements sandwiched between raceways in bearing rings. Rolling elements take many forms, including spherical balls, rollers or various other configurations, such as cone-shaped tapered rollers or barrel-shaped spherical rollers. Bearing rolling element guides, or cages, retain rolling elements within a bearing assembly, while typically allowing for free rotation of the rolling elements within the cages, and rotation of the cages within the bearing assembly. Cages can be used to separate rolling elements from each other, generally at equal intervals, and hold rolling elements in alignment with respect to the bearing rings. Depending on the structure of the bearing, or the bearing design, cages may be linear or circular and made from a variety of materials, including, but, not limited to brass, steel, and various types of plastic.
In some applications, such as for balance shafts for internal combustion engines, a rolling element and cage assembly can be used without discrete bearing rings, with the balance shaft and surrounding engine housing or block acting as inner and outer raceways, respectively. In other words, rolling element raceways are integrally formed on the outer diameter of the balance shaft and the inner diameter of the balance shaft housing or block, respectively. In this form, the cage retains the rolling elements within the cage pockets during assembly and operation.
Broadly, there are two main types of bearing cages; “crown” or “snap” cages; and “ribbon” or “riveted” cages. The “snap” type has an annular side member and axial partitions projecting from said member. These partitions are typically parallel to each other and have open rolling element pockets, allowing said rolling elements to seat or “snap” into position within these open pockets. The “riveted” type is comprised of two pieces or halves, each half with an open pocket to accommodate a rolling element. The halves are assembled on opposite sides of the rolling element, the pockets surrounding the rolling elements, and contact at land surfaces at intervals between rolling elements, then are joined together at the mating surface using various types or fastening elements, such as rivets. When rolling element bearings are used in balance shafts, typically cages of the “snap” type are used.
Cages are guided by one of the available surfaces between the inner and outer rings. Cages may be guided by the inner land or surface, wherein, the cage's bore slides, or is guided by, the outer diameter of the inner ring. They may also be guided by the outer land, wherein, the cage's bore slides, or is guided by, the inner diameter of the outer ring. Finally, cage's may touch neither ring, and be guided by the rolling elements themselves.
Some example bearing cages are shown in U.S. Pat. Nos. 6,247,847, 5,154,401 and 4,004,840.
Different types and sizes of bearings require specifically designed bearing cages, taking into account bearing assembly size, operating conditions, and rolling element size, among other factors. It is understood that a particular design of bearing may incorporate a type of cage, but, may require variations in the cage to accommodate the specific bearing, for example choice of rolling element or material used. In balance shaft applications, the balance shaft has a number of diameter variations along its length as a result of balancing masses and mounting features on the balance shaft that prevent a bearing or cage and rolling element assembly from sliding along a length of the shaft during assembly. Therefore, the cage and rolling element assembly is typically wrapped around the shaft, which, in turn requires that the cage be separable and flexible, in order to return to its required cylindrical form. A cage with increased flexibility is needed.